As Jaffa Cake said, to change icons, CandyBar is your best bet, or ShapeShifter (however this also changes, well, everything about your Mac - colour schemes, wallpapers, system wide themes).
You can download icon 'packs' and choose which ones you want to install. You can revert back to the original icon by dragging it off the current icon in CandyBar. I wouldn't recommend the Command + I option, as I did this to ALL my system icons back when I first started using a Mac, and it took HOURS to complete, and HOURS to reverse.
Also, to change your dock, download ClearDock 1.3. It can make your dock clear, as the name says, or let you recolour it - the shadow colour, the outline, the dock itself, and the arrows under open applications.
I love it set to clear, but at the moment, I have changed it to a mid-graphite setting, with a white border and white arrows, it looks very nice against my desktop.
Good luck personalising your new Mac, buddy.